a. Field of the Invention
This invention relates generally to collision avoidance systems and, more particularly to collision avoidance systems for aircraft and other forms of transportation, in which certain sensor parameters are variable depending on speed and attitude of the vehicle and other factors.
b. Description of Related Art
Due to its particular relevance to the emerging field of unmanned aircraft, the present invention will be described herein largely with reference to the exemplary applications of Unmanned Air Vehicles (UAV) and Unmanned Combat Air Vehicles. (UCAV). It will be understood, however, that the invention is equally suited to other vehicular applications such as manned aircraft, seagoing vessels, and road and rail vehicles, for example.
Operation of UAV""s/UCAV""s in the National Air Space (NAS) and/or Special Use Airspace (SUA) requires a collision avoidance system that meets Federal Aviation Administration (FAA) requirements for maimed aircraft. Since the UAV/UCAV is remote the operator does not have direct visual contact with the vehicle""s surroundings, and in the absence of an effective automated sense and avoid system may not be able to avoid a collision with other aircraft or with terrain objects (e.g., buildings, power lines, trees and so on).
Presently, the collision avoidance system must provide at least the same level of capability as manned aircraft operating under Visual Flight Rules (VFR), as stated by the FAA. However, the skies are becoming increasingly congested so that relying on human eyesight for collision avoidance is no longer adequately reliable. In addition, the FAA has developed a strategic plan to improve safety that includes a goal of reducing U.S. aviation fatal accidents by 80 percent from 1996 levels by the year 2007. Consequently, a joint FAA/Industry Support Group, under the aegis of the Association for Unmanned Vehicle Systems International (AUVSI), has stated the need for solutions that address the concerns of both the UAV/UCAV industry and the FAA. The goal is an Advisory Circular (AC) that assures UAV/UCAV operations that meet the fundamental requirements of the FAA, but which do not unduly restrict UAV/UCAV operations in the NAS. As one means toward this end, Paragraph 8.(4)-(n) of a draft AC requires UAVs to be equipped with xe2x80x9c. . . a means to xe2x80x98see and avoidxe2x80x99 equal to, or greater than, a manned aircraft.xe2x80x9d
Although all are agreed that increasingly capable sense and avoid systems are needed for UAV""s/UCAV""s, there are many practical factors that must be taken into account in order for such systems to be feasible. For example, the size, cost, efficiency and (sometimes) expendability that are key advantages of UAVs/UCAV""s dictate that the use of systems that are reliable but also inexpensive, compact and lightweight.
Conventional collision avoidance systems used with manned aircraft do not offer truly satisfactory solutions for UAV""s/UCAV""s. In particular, conventional systems for avoiding air traffic collisions utilize Traffic Collision Avoidance System (TCAS) transponders or visual sensors that are excessively large, heavy, costly, complex and are in other respects unsuitable for most UAV""s/UCAV""s. For example, standard TCAS equipment is unable to interact with non-cooperating objects and typical low flying obstacles, such as birds, which may be invisible to the radar. In addition, the equipment is costly and, in most cases, exceeds the limited weight and size capabilities of most UAV""s/UCAV""s. Of course, while acute with UAC""s/UCAV""s, these are important concerns in the case of manned aircraft as well.
Methods that have been proposed to address these problem include the use of forward-facing mounted television cameras on the wings of the aircraft, as shown in U.S. Pat. Nos. 5,581,250, and 4,918,442. An inherent limitation of this type of system is the fact that it is based on an active light source, which is not passive/stealthy and is therefore unsuitable for many military applications. Furthermore, the monitored airspace is limited to the area directly in front of the aircraft. The systems disclosed in U.S. Pat. Nos. 4,755,818 and 5,321,489 utilize laser beam technology but exhibit similar drawbacks, and also require that compatible equipment be installed on a second, cooperative aircraft in order for the aircraft to be detected by the system.
Accordingly, there exists a need for a sense and avoid collision avoidance system which is reliable and capable of autonomous or semiautonomous operation. Furthermore, there exists a need for such a system having a capability that meets and exceeds the capabilities of an aircraft operating under visual flight rules (VFR). Still further, there exists a need for such a system which is lightweight and compact, and which optimizes the employment of its sensors so as to maximize efficiency and minimize power and space requirements. Still further, there exists a need for such a system that is able to function using a minimum of active sensor transmissions, so as to be sufficiently passive/stealthy for military vehicles and related applications.
The present invention has been developed to address the specific problem of providing UAV""s/UCAV""s the same level of capability and reliability as a manned aircraft operating under VFR per FAA requirements within NAS and SUA. However, the invention is not limited to UAV""s/UCAV""s, as other applications exist for this invention such as the commercial airline industry, private aircraft, helicopters and ground and marine transportation to name but a few.
The system includes passive and active sensors and a control system designed to prevent mid-air and/or ground collisions. In addition to flight-path obstacles, this system performs other obstacle sensing operations such as detecting ground-based obstructions, undesirable weather and unmapped objects. The system is compatible with existing UAV/UCAV sensors and is able to detect non-cooperative targets. The system is also capable of functioning autonomously, and in a stealth mode if necessary.
In a preferred embodiment, the invention uses an infrared (IR) camera as the passive sensor and Light Detecting and Ranging (LIDAR) or Laser Detecting and Ranging (LADAR) as the active sensor to detect obstacles within a substantially 360xc2x0 spheroid volume (envelope). The envelope extends about a centroid that is spaced from the aircraft by a distance and direction that is a function of the speed and direction of motion of the aircraft and the time required for executing a predetermined evasive maneuver. The size and shape of the envelope is consequently variable depending on the speed and attitude of the source aircraft and other factors, as by increasing/decreasing sensor power or output, or aligning threshold values, for example. Any object entering the envelope will generate data that is transmitted to the receiver, creating an autonomous unit not requiring installation of additional hardware on the target aircraft. Once the data is received, the collision avoidance computer is immediately informed that there is a hazard and a signal is sent to the autopilot or other autonomous control mechanism and a collision avoidance maneuver is executed.
The variable envelope enables the configuration of the sensors and/or the data processing to be adjusted for maximum efficiency. For example, the envelope may be adjusted to extend further ahead of the craft at higher speeds or to extend more downwardly for descending aircraft and more upwardly for ascending aircraft. Because sensor range/output is thus maximized in those directions that are most important based on the speed and attitude of the aircraft or other vehicle (e.g., in those directions presenting the highest closing rates), but not in other directions which are less important (e.g., those directions having slower closing rates), the complete system, including the power supply, can be lighter, more compact and less expensive as compared with a system that maintains an envelope at maximum range all about the vehicle at all times.